A replaceable toner cartridge is used for a laser printer. Such a toner cartridge accommodates a certain amount of toner so that toner is supplied from the toner cartridge to a printing unit for printing. When the toner cartridge runs out of toner, the used toner cartridge is replaced with a new toner cartridge.
Japanese Patent Application Publication No. H11-125999 proposes a laser printer which employs a lower developing bias and a lower laser power than in its normal operation so as to lighten printing density The proposed laser printer provides a toner-saving mode for reducing toner consumption by forcibly thinning out dots (reducing the number of dots). If the toner-saving mode is used to reduce toner consumption, it is possible to delay replacement time for replacing the toner cartridges due to toner exhaustion.
The toner cartridge includes various rotary components such as an agitator for agitating toner and a gear for transferring driving force to the toner cartridge. The replacement time of the toner cartridge is also determined based on lives of the rotary components (a rotation driving time calculated on a predetermined number of pages to be printed, or a maximum time in which the rotary components can be used).
Therefore, even if the toner-saving mode is used to reduce an amount of toner to be consumed, the toner cartridge needs to be replaced when the replacement time based on the lives of the rotary component arrives before toner exhaustion. Hence, the replacement time of the toner cartridge cannot be delayed. Further, toner left in the toner cartridge is wasted when the toner cartridge is replaced due to an end of life of the rotary components.